Variable inductance



- Oct. 10, 1939. H, N Buss 2,175,554

VARIABLE INDUCTANCE Filed Nov. 14, 1936 ATTORNEY.

UNITED sTATEs PATENT o1=1=1cEl VARIABLE INDUCTNCI llaroidN.Bli.,lthaca,N.Ya-ignor Research Horse corporation oi' New York tomblthaca, NrY.. a

museum November 14, me. sum N.. nnss s can. (c1. 111-119) This invention relates to electricity, and particularly to a variable coil of compact construction capable of a great range of variationin inductance through continuous fine gradations,

5 without the use of switches. In my prior Patent No. 2,037,061, issued April i4, 1936, I described a variable coil whose effective length could be readily changed by any small fraction of a turn, without theA use of extraneous reeling coils, so that it 1o could be mounted as a unitary device. The presy ent invention is an improvement thereon, and is generally applicable to various scientific and commercial applications, wherever fine gradations in the length or number of turns of a coil l5 are desired, with a wide range of variation. It is particularly applicable to the radio art, as it makes possible the practical manufacture of al1- wave receivers without the multiplicity of coils and band switches with which they are at pres- 20 ent encumbered. The invention also gives easier tuning and more efficient reception.

In the ordinary radio receiver, tuning to the various wave lengths'has generally been done by turning the condensers to various degrees of caz5 pacity C. It has long been r that for ideal reception the inductance coils (controlling the inductance L), should also be varied for various wave lengths, in order to maintain desirable L/C ratio; but as a practical matter it has been l found diillcult to make variable coils of reasonable size and good characteristics, and consequentlyv the use of fixed inductance coils has remalned standard practice on commercial receivers.

l Fixed inductances L approximating' the desired value have been used in conjunction with variable condensers C, and in practice could cover a fair range without the. L/C ratio bec so bad as to spoil reception. While the ce lo in receptioncould be tolerated in the ordinary broadcast range, it was found that the diiiicultiesl increased with the shorter wave lengths, so that the same coils could not be used, and it has been commercial practice to then substitute other L5 nxed coils, with attendant switches and complexity. so that 'a commercial universal or all-wave receiver has become a very complicated device.

f- The present invention therefore hasa particular application. to short-wave radio, in that it Opermitsafewsimplecoilstotaketheplaceof many, and with better results, since the few variable coilsattain with .precision the desired L/C ratio which the many iixedcoils only approximated. With the improvements to be described I it is possible to make a so-called "al1-wave radio receiver which can be tuned from ordinary long wave broadcast range down to the short waves for foreign reception without a break or switch. all on the same simple set .of coils.

Asfrom my prior patent above 5 mentioned, the present invention extends the rangeby varying the core as well as the coil, reduces the diameter, shortens the apparatus by eliminating the longitudinal travel of the coil sleeve. and provides an improved transfer mechanm for leading the wire from one end of the core to the other.

Referring now to the drawing:

Fig. l is a side elevation of one of the coil units, showing the variable coil and transfer mechanism. l

Fig. 2 is a cross sectional view of the sleeve on which the coil is wound and unwound, showing the internal construction including the movable iron core. 2o

Fig. 3 is a cross-section on line 3--8 of Fig. l, showing the feather key, and the transfer mechanism, from which, in conjunction with Fig. 1, it

-can be seen that it has a diagonal position.

Similar reference numerals refer to similar parts throughout the various views.

Referring now to Pig. l and Fig. 2, the movable wire I is wound on an insulated sleeve 2, which is preferably made of rubber, Bakelite, or some similar material, this insulated sleeve 2 prefer- 30 ably being provided with' screw threads I to receive and guidethe wire I in its winding and unwinding. The end of the wire I is secured to a central pivot pin 4, as shown in Fig. 2, which passes through an'insulaied plug t to a pivot 35 bearing 6, which is insulated from the frame 1 by the insulating. bushing l of rubber, Bakelite, or other suitable material. This pivot bearing I provides the electrical take-off for the end of the The other end of the insulated sleeve 2 is preferably provided with a sleeve l of brass orother conducting material on which the other end of the wire I is wound and unwound. This brass sleeve l short circuits the turns of wire I wound on it, so that they are inactive. An insulating bushing Il insulates the brass sleeve 0 from the pivot Il, which turns in the pivot bearing Il, thus supporting the right hand end of the sleeve 2. 50

The transfer forcarryingthe wire I quickly from the active end to the inactive end preferably consists of a metal tube Il of iine bore, suihcient to easily accommodate the wire I, this tube IlbeingbentinaU shape andplacedso as to diagonally straddle the sleeve `2 and 9. This is shown in Fig. 1 and also in Fig. 3, which is an end view. While a tube is preferable, a U-shaped slot or groove in a segment may be used, or anyother element guiding the wire I in the same general manner. When the wire I is threaded through the tube I0, the wire I is carried from one side-such as the front in Fig. l-diagonally to the other side-or back of the sleeve 9 in Fig. 1-at the same time being carried along the length of the sleeve a sufcient distance so that no objectionalble self-induction eiects are set up between the coils at Athe two.

ends. f The tube I is rotatably and slidably mounted in the bearing sleeve I2 by means o the pivot pin Il, which is held in place by the tension of the coil springs I5. These springs I5 tend f to pull the U tube I0, downward as shown in 'Fig l, or awayl from the sleeve 2, and thereby maintain the wire I at a suitable tension for winding or unwinding. The tube I@ can also oscllate or rotate to a certain extent about the pin ld as a pivot. This allows the tube l0 to adjust itself to the position of the wire (i as it leaves the sleeve 2, and gives.a free running mechanism capable of guiding the wire l into the grooves 3. e

The tube it and pivot pin bearing l2 are mounted on the threaded block 20, which also carries the primary coil 2l., This threaded block 2t ls-carried 'by the screw 2i', whose pitch and hand are such as correspond in action to the thread 3, so that the transfer tube l@ and prt mary coil 2l are caused to follow the pitch ot the wire winding on the thread 3. Tlfius the primary di is maintained constantly adjacent the last turn of the active coil oi the wire l., Toe actual pitch and hand oi the respective threads will of course depend on the gearing 23 sonnentu ing them, which may vary' in difzferent tions, as will be apparent to those skilled the art. The loul or grounded end ot the coll be led in through the wire 2S.

When the coil is used in a circuit leaving automatic volume control, the bearing sleeve l2 'l insulated from the grounded framework l by the insulation 2l; the wire ,25 may then be attached to the automatic volume control circuit, as will be apparent to those skilled in the art. For the same reason, the sleeve t is insulated so as to have no electrical contact to the framework l. The pivot 3 l which supports the right hand end ci the rotatable sleeve 2,' is hollow, and through its opening passes the fixed rod St, locked to the frame l' by the set-screw This fixed rod @Il -ls provided with a screw-thread 34' inside the sleeve @n this screw-thread 34 is mounted a nut or hub llt, provided with corresponding screw threads to run on the screw 3Q', and having projecting keys 38 to engage two splines or lzeyways to Acut inside the sleeve t, so that the hub 36 will rotate with the sleeve 2 and so be screwed up and down the rod 34. The hub 35 is loose enough Y to slide freely within the sleeve 2, but owing to the keys 38,.must revolve with it, so as to be screwed longitudinally.

The hub 36 carries a magnetic core l0 of radio irequency iron core material having lowhysteresis, such as has been specially developed for high frequency work as is well known in the art in stationary coils. This radio frequency ironv core 40 is mounted on a tubular projection 4I of the hub 35, through which the screw 34 may pass.

The pitch and yhand of the threads 2l' and SAT-in conjunction with whatever gearing used between themare so proportioned and selected that when the variable coil Itis wound to its full number of turns the iron core It is moved to the left in Fig. 1 soas to be fully inserted in the variable coil I; and when the variable coil I is unwound to a few turns the iron core lll'is withdrawn back to the right-hand end of the sleeve 2, so as to be removed from the field of the coil I, so that it may have its minimuminductance. In other words, as the variable coil l iswound larger, the core Il! is gradually inserted to assist in increasing the inductance, and as the coil l is unwound'the core 40 is gradually withdrawn to assist in diminishing the inductance.

By this simultaneous combined action of a variable .coil and variable core, a very lrapid and smooth change of inductance is made possible, thus creating a variable coil of very high etliciency. By this means a relatively small coil may be made to cover a very large range of useful inductance, and much more simple and compact radio sets can be constructed. The presence of secondary at those frequencies, a valuable feature u asv the primary coil must be small enough to be elcient at the highest frequencies encountered. ln my prior patent above mentioned it will bc noted the sleeve il moved longitudinally during the winding while the primary 2I and transfer mechanism ill were stationary, whereas in the present form the sleeve 2 is fixed longitudinally andthe primary 2l and transfer mechanism I0 are ted along; thus the total length of the mechanisse is considerably shortened in the present torni, which with. the reduction in diameter above described permits a very compact device.

While l have in the foregoing described certain specific examples, it will be understood that they are merely for purposes of illustration, to maire clear the principles of the invention, which is not limited to the particular forms shown, but is susceptible to various modifications and adaptations diferent installations, as will be apparent to those skilled in the art, without departing from the scope of the invention as stated in the following claims.

what l claim A variable incluctance device, including in combination a coil, means for winding and unvvlnding a variable number of turns of said coil, a magnetic core, and means for inserting the magnetic core simultaneously with the winding and withdrawing the magnetic core simultaneously with the unwinding, so that when the coll is substantially wound the core is strongly inductively associated therewith, and when the coil is unwound to a iewturns the core is withdrawn to such a distance as to have little effect on the inductance o the coil.

2. ln a variable inductance, the combination of a primary coil, a variable secondary coil coupled thereto, means for winding and unwinding said secondary coil to give various degrees of inductance, a movable magnetic core, means for movsleeve in various degrees to' form a variable coil, a magnetic core located within said sleeve. and means for moving said core axially relative to the coil and simultaneously with the variation in the coil, the axial motion of the core relative to the y coil being in a direction opposite to that in which the said member and simultaneously unwind from the A other end, means for rendering the coil at one end inactive while the coil at the other end is active. and transfer means for carrying the wire between the active to the inactive coils comprislng a `Ushaped guide located diagonally relago tively to the space between said coils and arranged to take the wire from one side and return it to the other side oi' said rotatable member, so that as it is unwound from one end it will wind up on the other end.

5. In a variable inductance, a rotatable member, a coil o! wire arranged to wind on one end ot said member and simultaneously unwind from the other end, means for rendering the coil at one end inactive while the coil at the other end is active. and transfer means i'or carrying the wire between the active to the inactive coils comprising a U-shaped guide, partially embracing said rotatable member in a diagonal direction so as to take the wire from one coil and feed it to the other coil on the opposite side oi' the rotatable member, whereby the wire may be interchanged between coaxial coils with the same direction o! rotation. p

8. In a variable inductance. the combination of a variable coil oi wire, a rewinding coil coaxial with the mst-mentioned coil, and a transfer means for carrying the wire between the two coils,

said transfer means comprising a U-shaped guide picking up the wire as it leaves one side oi' one coil and guiding it diagonally so as to deliver it to the other side of the other coil, said wire sliding ,through said guide with frictional contact, and

means for keeping said wire under tension.

7. In a variable inductance, the combination of a winding drum, a rewinding drum, wire arranged to wind and unwind between said drums to i'orm a variable inductance, a curved guide for said wire for' transferring it from one drum to the other, said guide extending diagonally and partially embracing said drums, and yieldable means for urging saidl guide away from said drums, whereby the wire is maintained under tension.

8. In a variable inductance, the combination of a variable coil of wire, a rewinding coil, a transfer means between said coils comprising a curved guide external to said coils and placed diagonally so as to take the wire from one side oi one coil and deliver it to the other side of the other coil, a pivot for said guide about which it may oscillate, and spring means tending to move said guide away i'rom said coils, whereby the wire is maintained under tension.

9. In a variable inductance, the combination of a variable coil of wire. a rewinding coil, a transfer means between said coils comprising a curved guide external to said coils and placed diagonally so as to take the wire from one side o! one coil and deliver it to the other side of the other coil, yieldable means for urging said guide away from I said coils to maintain the wire under tension, a

magnetic core movable relative to the variable coil oppositely to the direction in which the coil is winding. so that when the coil has a i'ew turns the core is withdrawn from it to reduce the inductance, and when more turns are wound on the coil the magnetic core is simultaneously increasingly inserted therein, so as to create a rapid rate of increase in the inductance.

`HAROLD N. BLISS. 

